In general, what is known as a magnetic recording method to be used for a magnetic record regeneration system such as a magnetic card reader and so on is an FM modulation method, in which binary magnetic data is recorded into a magnetic recording medium by applying combination of two kinds of frequencies, namely F and 2F. When reading out the magnetic data that has been recorded by the FM modulation method, a magnetic head is slid relatively against a magnetic stripe on the magnetic recording medium to regenerate the magnetic data as an analog regeneration signal, with which the binary data becomes demodulated.
Regarding the demodulation process, concrete explanation is given by using FIG. 11 and FIG. 12. FIG. 11 is a block diagram to show an electrical structure of a circuit that puts the demodulation process into practice by the FM modulation method. Meanwhile, FIG. 12 includes drawings of signal waveforms, each of which relates to its corresponding position in the circuit shown by FIG. 11. That is to say; the signal waveforms of (b) to (g) in FIG. 12 show those at the positions of (b) to (g) in FIG. 11. Incidentally, the signal waveform of FIG. 12(a) is a signal waveform of a record signal saved in a magnetic stripe of a magnetic card 102.
In FIG. 11 and FIG. 12; a magnetic head detection signal (Refer to FIG. 12(b)) obtained by sliding a magnetic head 101 relatively against the magnetic stripe on the magnetic card 102 is processed at first so as to remove high-frequency noise by using a band pass type filter, i.e., BPF (Band Pass Filter) 103 (Refer to FIG. 12(c)), and subsequently the signal being as BPF output is input into an amplifier 104. Then, the BPF output amplified by the amplifier 104 is input into a peak detection circuit 105. After peak detection is carried out there (Refer to FIG. 12(d)), zero cross point detection of the peak detection signal is carried out in a comparator 106a (Refer to FIG. 12(e)). On the other hand, the BPF output amplified by the amplifier 104 is also input into a comparator 106b in order to carry out zero cross point detection of the BPF output through comparison with a zero level (Refer to FIG. 12(f)). Finally, a timing generation circuit 107 outputs a signal that has a signal level of the output signal of the comparator 106b at each changeover timing from/to Hi-level and to/from Lo-level of the output signal of the comparator 106a (Refer to FIG. 12(g)). Thus, the signal waveform of FIG. 12(a) is obtained to complete the demodulation process.
In this sample case, a differentiation circuit is used as the peak detection circuit 105 in FIG. 11 and FIG. 12 (Refer to FIG. 12(d)). However, operation only with the peak detection circuit 105 as a differentiation circuit does not work out adequately sometimes. For example, if a passing speed of the magnetic card 102 in relation to the magnetic head 101 suddenly becomes slow, change in an analog regeneration signal by magnetic reversal becomes so small that the peak detection signal shown by FIG. 12(d) results in a signal with small peak values as the solid line shows in FIG. 13(d). Consequently, in the output signal of the comparator 106a there are generated a couple of so-called saddles SD1 and SD2 (Refer to FIG. 13(e)), and an irregular signal shown by FIG. 13(g) is input into a CPU 107 to cause a read error.
To avoid such a bad influence by the saddles SD1 and SD2, sometimes an integration circuit is used instead of the differentiation circuit as the peak detection circuit 105. In that case, an output signal of the integration circuit results in a signal waveform as the dotted line shows in FIG. 13(e). Then, zero cross point detection is carried out through comparison with a zero level by the comparator 106a, in the same manner as an operation using a differentiation circuit; and eventually it becomes possible to avoid the bad influence by the saddles SD1 and SD2 shown in FIG. 13(e). However, when such an integration circuit is used, it may become difficult to detect a peak in a signal with a long time-interval and a low-frequency noise may come up due to noise accumulation. As a result, there exists a chance of a read error because of another reason that is different from the problem of the saddles SD1 and SD2 described above.
Thus, taking into account that it is difficult to maintain a sufficient reading accuracy in a magnetic data read circuit in which only one of the differentiation circuit and integration circuit is built in; a magnetic data read circuit, where both of the differentiation circuit and integration circuit are built in, is being developed. For example, in the magnetic data read circuit that FIG. 14(a) shows, there is placed an analog switch 109 (a relay, etc.) for selecting one of a differentiation circuit 105a and an integration circuit 105b in the circuit so that a changeover is made between the differentiation circuit 105a and the integration circuit 105b by sending a selection signal, as required, to the analog switch in order to enable reading the magnetic data with optimum circuit condition. Furthermore, if a read error comes up while peak detection is carried out by the differentiation circuit 105a (or the integration circuit 105b), it is possible to try reading the magnetic data again while changing to the integration circuit 105b (or the differentiation circuit 105a, respectively) by sending the selection signal described above.
Furthermore, there is developed another magnetic data read circuit, in which no changeover between the differentiation circuit and the integration circuit is made but output signals from both the circuits are synthesized for improvement of reading accuracy (For example, refer to FIG. 14(b) and Japanese Unexamined Patent Publication (Kokai) No. 62-234205, incorporated herein by reference). In a magnetic data read circuit shown by FIG. 14(b), there is placed a subtraction circuit 110, by which the output signal of the integration circuit is subtracted from the output signal of the differentiation circuit. As a result, it becomes possible to prevent any of so-called saddles from coming up in an output signal of the comparator 106a (Refer to FIG. 13(e)), and eventually to avoid any read error.
Incidentally, other demodulation methods in addition to the method shown by FIG. 14(b) in which both the output signals of the differentiation circuit 105a and the integration circuit 105b are used; include, for example, a method where the output signal of the integration circuit 105b is used as a gate signal to the differentiation circuit 105a (Namely; an AND operation between the output signal of the differentiation circuit 105a and the output signal of the integration circuit 105b is considered), and another method using a circuit where the output signal of the differentiation circuit 105a and the output signal of the integration circuit 105b are compared and integrated (For example, the output signal of the integration circuit and an F2F signal are synthesized by a circuit of a diode and so on, and then the newly synthesized signal is used as a gate signal to a circuit where the output signal of the differentiation circuit becomes the data).
However, in the circuit described above where demodulation is carried out by a changeover between the differentiation circuit and the integration circuit as required; if once a read error occurs, it becomes necessary to change from the circuit being selected at the time to the other circuit between the differentiation circuit and the integration circuit, and then read again the magnetic data. Therefore, it is required to transfer the magnetic card again, and namely it is difficult to read the magnetic data with high accuracy through “One-and-only” transfer of the magnetic card.
Furthermore, also in the circuit where demodulation is carried out by using both the output signals of the differentiation circuit and the integration circuit; if once a read error occurs, it is necessary to read the magnetic data again through the same circuits. Therefore, it is required to transfer the magnetic card again, and as described above, namely it is difficult to read the magnetic data with high accuracy through “One-and-only” transfer of the magnetic card. In particular, when reading the magnetic data is carried out again under the same circuit condition, there is a strong possibility of another read error because of no hardware-wise change in reading conditions.